The introduction of adhesive systems has brought a significant change to dental restorative dentistry in the sense that they enable procedures that are minimally invasive and also that are able to protect the tooth structure better.[1] Dental adhesives have now become the foundation of modern restorative dentistry since they provide the long-lasting bonding of the composite resin and enamel or dentin, which has a direct impact on the life of the restoration and its success.[2] Although progress has been made in commercial adhesive systems, issues like hydrolytic degradation, polymer breakdown at the adhesive interface, sensitivity of the techniques, and inconsistent clinical performance still hamper long-term outcomes.[3] It is reported in studies that adhesive restorations can have an average clinical survival of about 5-8 years, and secondary caries and bond failure are among the most frequent causes of failure.[4]

The worldwide trend is towards more adhesive restorative procedures as dental caries are on the rise and the popularity of tooth-colored restorations grows.[5] This burden is also enhanced by a lack of access to high-level imported dental materials and their high prices in low- and middle-income countries, such as Pakistan, where they are not generally widely used in the clinics. Consequently, most dental practitioners depend on imported adhesive systems, which might not be best suited to local clinical conditions, such as local humidity, operator handling, and biological factors related to the patients.[5] Regional studies have demonstrated considerable differences in shear bond strength of various adhesive systems applied to teeth of Pakistani patients, thus indicating the importance of evaluating bonding materials contextually.[6, 7]

Besides bond strength, biocompatibility has become a key factor in the choice of adhesives because the unreacted monomers and chemical components can have cytotoxic effects on the pulp and other tissues.[8] Moreover, shear bond strength is another important mechanical factor of clinical success because poor adhesion results in microleakage, marginal failure, and debonding of restoration under functional loads.[9] Thus, a perfect dental adhesive has to exhibit high bond strength, durability over a long period, and high biocompatibility with a simple clinical practice.[10, 11]

Although a lot has been done on commercial adhesive systems, there is still a wide gap in development and scientific validation of indigenous dental adhesives, which are cost-effective, biocompatible, and clinically effective. Formulations designed locally may have the potential to decrease reliance on imported materials and provide performance that is specific to local clinical requirements. There is, however, little evidence on their mechanical and biological performance, especially in their shear bond strength and cytocompatibility in standardized conditions. Thus, the current research is intended to evaluate shear bond strength, biocompatibility, and clinical effectiveness of native dental adhesives and their comparison with standard commercial systems.

The study was carried out as a comparative experimental study, which was a laboratory study where indigenous dental adhesive formulations were compared to a standard commercial adhesive system to determine shear bond strength, biocompatibility, and clinical efficacy. The entire period of the research was one year from April 2025 to October 2025, during which specimen preparation, laboratory testing, and data analysis were performed in consecutive stages.

The sample size was determined based on the OpenEpi software (version 3.01) through the use of the formula to compare two independent means, with shear bond strength as the main outcome variable. The average shear bond strength of an industrial adhesive was reported to be about 18.5 ± 4.2 MPa.[12] The sample size was estimated to be 64 specimens per group with an assumed minimum detectable difference of 2 MPa between groups, 95% confidence interval, and a power of 80%. The final sample size was modified to 70 specimens in each group, which led to 140 samples.

The selection and preparation of extracted human premolars collected because of orthodontic reasons were selected using a non-probability consecutive sampling technique. The teeth were chosen based on some set eligibility criteria and randomly divided into two groups, which were the indigenous adhesive group and the commercial adhesive control group.

Inclusion criteria included human permanent premolar teeth, freshly extracted and with intact buccal enamel surfaces, caries, cracks, restorations, fluorosis, and structural defects. Teeth that had been extracted recently (within the range of three months) and kept in the right conditions in thymol solution were added to preserve the integrity of the structures. The teeth that had similar anatomy in terms of their crown morphology were chosen to provide uniformity of bonding surfaces. The exclusion criteria were teeth with enamel hypoplasia, developmental defects, apparent cracks or fractures, prior chemical treatment, root caries up to the crown, or history of endodontic treatment. The teeth depicting dehydration, surface contamination, or any other unfavorable storage environment also did not make it to the study to avert bias in the bond strength outcome.

To collect the data, the chosen teeth were scaled of debris and soft tissue remnants with an ultrasonic scaler, and kept in distilled water until further use. The surfaces of the buccal enamel were made smooth using silicon carbide abrasive paper to provide a uniform bonding area. All the specimens were cast in blocks of acrylic resin to facilitate handling. In the experimental group, the indigenous dental adhesive was applied in line with the protocol of a manufacturer, whereas in the control group, a commercial adhesive system that is commonly used was used with the same protocols. The treated enamel surfaces were then bonded to composite resin cylinders using a standardized cylindrical shape mold and cured over a fixed time period with the help of an LED light-curing unit.

Indeed, shear bond strength testing was conducted on a universal testing machine with a load applied to the crosshead at a speed of 1 mm/min until failure ensued after storage in distilled water at 37 oC in a 24-hour period. The highest value of the force at debonding was noted in Newtons and converted to megapascals (MPa) to be analyzed statistically. The biocompatibility was tested by in vitro cytotoxicity assay on a fibroblast cell line, wherein the viability of the cell line was tested following exposure to adhesive extracts. A short-term follow-up in vivo pilot evaluation was conducted to evaluate clinical efficacy through the retention, marginal adaptation, and post-operative sensitivity.

Data obtained were keyed and analyzed with SPSS version 26. Shear bond strength and percentages of cell viability were quantitative and were expressed as mean standard deviation. The Shapiro-Wilk test was used to determine the normality of the data. The independent sample t-test was used to compare the mean shear bond strength and biocompatibility results of the two groups. A p-value of 0.05 or less was taken as significant.

The average shear bond strength was a bit less in the native adhesive group than in the commercial group; though, no significant difference between the two systems was noted (p = 0.214), showing similar bonding behavior of the two systems.

Table 1: Comparison of Shear Bond Strength between Indigenous and Commercial Adhesive Systems

The indigenous adhesive group showed a significantly higher level of cell viability as compared to the commercial adhesive group (p = 0.036), which means that it was more biocompatible and less cytotoxic.

Table 2: Biocompatibility Assessment Based on Cell Viability in Fibroblast Culture

There were no statistically significant differences in retention, marginal adaptation, sensitivity, or failure rates between the two groups, and both exhibited high clinical success rates (p > 0.05). The indigenous adhesive, however, had a slightly better overall pattern.

Table 3: Clinical Performance Outcomes after Follow-Up (3 Months)

biocompatibility, and clinical performance in the short-term of an indigenous dental adhesive system with a conventional commercial adhesive. In general, the results indicated that the native adhesive had similar shear bond strength to the commercial one, but tended to be much more biocompatible regarding fibroblast viability. Both systems showed high retention and acceptably marginal integrity levels, with the trends being slightly better in the indigenous group, though the differences were not statistically significant. The current research indicated no significant difference between native and commercial adhesives in terms of shear bond strength. The current study is consistent with Hardan et al. (2021), who, in a systematic review, reported that universal and modern adhesive systems tend to have similar dentin bond strength irrespective of adhesive composition and application strategy variations, provided that standardized bond.[13]. There is, however, some variation in the literature that has been reported in terms of bond strength results. Miljkovic et al. (2022) also discovered that conditions during curing and polymerization parameters could considerably affect the performance of adhesives, resulting in variation in bond durability across various systems.[14] Bourgi et al. (2023) also found that contamination in the bonding process might decrease bond strength irrespective of the type of adhesive used in the study.[15]

In terms of biocompatibility, the current experiment showed that the fibroblast viability was significantly higher in the native adhesive group than in the commercial adhesive system, indicating less cytotoxic capacity. These results are in line with those of Pagano et al. (2021), who have indicated that some commercial adhesive systems can have certain cytotoxic effects on human gingival fibroblasts depending on the monomers and residual solvent contents.[16] Similar patterns were also observed in a 2024 study in which cytotoxic activities were reported to be dependent on the type of solvent and adhesive viscosity but not bonding efficacy.[17]

This enhanced biocompatibility of the native adhesive could be due to possibly reduced levels of cytotoxic monomers or higher polymerization efficiency, leading to less leaching of the remaining constituents. The clinical implications of these findings are that adhesive toxicity severely affects pulp and periodontal tissue response, particularly in deep cavities, where there is a decrease in dentin thickness.

Both adhesive systems showed high short-term success rates with good retention and marginal adaptation, clinically. These results are consistent with Staxrud and Valen (2022), who have found that universal adhesive systems demonstrate good clinical outcomes when used in composite repair and restorative treatment in short-term follow-ups, and that, in most cases, the adhesives are satisfactory when the adhesive bonding protocols are adhered to.[18] In general, the current research indicates that indigenous dental adhesives can provide a potential alternative to the commercial system, especially in resource-constrained environments. Although shear bond strength was the same, the better biocompatibility profile of the indigenous formulation is an added benefit in clinical usage. Nonetheless, there is a need to conduct long-term clinical trials to further confirm durability, hydrolytic stability, and performance under functional oral conditions.

Limitations:

The current research had its limitations, which ought to be taken into account when interpreting the results. This was an in vitro study and only a short term clinical evaluation was performed, which may not be a complete reflection of the long term performance of intraoral performance in complex oral conditions such as thermal cycling, masticatory stresses, and enzyme degradation. The sample size was quite small, and also was limited to extracted premolars, which may be a limitation to generalization to other types of teeth. In addition, the assessment of only fibroblast cell lines with regard to biocompatibility may not entirely mimic the whole biological response of pulp and periodontal tissues. The results should be validated with increased follow-up and multicentric clinical trials.

The indigenous dental adhesive showed the same shear bond strength as the commercial adhesive system but was much more biocompatible in vitro. Both adhesives had satisfactory short-term performance as indicated by the clinical performance and there were slightly positive trends in the indigenous group. Based on such findings, it can be argued that native adhesive formulations can be utilized as a cheaper and safer biologically beneficial substitute to commercial systems, in particular, in resource-constrained settings, though it is recommended that further long-term clinical trials should be conducted to verify that it is a cost-effective and clinically viable alternative.

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